An X-ray computed tomography (CT) apparatus is conventionally used for examination of myocardial perfusion. In the examination, for example, a contrast material is injected into a blood vessel, and CT images of a heart collected by the X-ray CT apparatus are analyzed. The amount of blood flow into the cardiac muscle is measured by estimating the amount of the contrast material reaching the cardiac muscle and estimating the amount of blood flow into the cardiac muscle based on the estimated amount of the contrast material.